DirtRider . Net MX, SX, Arena Cross, Off-Road Community

This is the text version of DirtRider.Net
Click Here for the Full Version

Pages: 1

WR400 myths and truths
(Click here to view the original thread with full colors/images)

Posted by: TexKDX---------------------

OK, it is time to perk up my almost new '98 WR400.  In doing the reaseach of what to do and what the results will be, I have come across conflicting information.

1) Throttle stop - one article says to cut it to 8.5 mm, not just remove it and throw it away.  Supposedly going too far past WOT confuses the ignition system and kicks in a rev limiter at 9,000 RPM amongst other bad things.

A noted thumper professional says this is bullhockey, that one difference between the WR and the WZ is the brain box and the WR has a rev limiter set at about 9400 RPM.  He says to just take it out and forget it.

2) - cam timing - The same thumper professional says to leave it along on the WR, that changing to YZ specs will soften the bottom and mid range power compared to stock and only help it where the motor can't go - above 9400 RPM.  Other sources say to change to YZ specs.  One riding buddy on the WR says the cam change was the single biggest improvement, even better than the Big Gun pipe.  Now he did the cam change AFTER installing the pipe.  DO they two work great together?  Is the cam change a bad idea with a Thumper baffle and stock pipe?

3) Jetting - Thumper professional says to go to a 172 main and 48 pilot for sea level - 1000 feet elevation.  Any other jetting suggestions?

Thanks all.  I hope to just rip into it once to do the throttle stop, jetting, cam change/no cam change, and replace the seat and tank.

Thanks all for your input.  Oh, the bike will be used for enduros, dual sport events, and agressive trail rides/training.  It is not my only enduro bike.

Posted by: Rich Rohrich---------------------

With all due respect to the above mentioned "professional" the weird cam timing on the WR was only done to balance pumping losses with the restrictive exhaust. Once you reduce the backpressure the cam timing is just WRONG. Anyone who thinks adding ~23 degrees to the Expansion stroke won't help bottom end isn't paying attention. The downside is you are adding ~23 of overlap as well, so you give up a bit of idle speed lugging ability, but the cylinder filling is improved at every point above about 2500 rpm. Better cylinder filling equals better torque. The Thumper insert should help a bunch, but using a YZ can works even better , and they can be had cheap because everyone seems to think you HAVE to change it because it's stock http://dirtrider-forum.com/forums/ubb/smile2.gif   I've found with the jetting that a 45 with a 1 clip position richer needle improves throttle response (pilot to needle transition) at sea level . A 48 works well at sea level when it's cool outside (below ~ 50), unless you are running straight pump gas with a high alcohol or oxygenate percentage. These motors are fairly insensitive to main jet size, so erring on the lean side is pretty safe and wakes up the upper rpm range.  Using a fast burning race gas like VP C-14 improves throttle response a TON, allows you to jet the pilot leaner in most cases and runs stronger at high RPM.

Keihn designed the carb with a stop. My guess is they did it for a reason http://dirtrider-forum.com/forums/ubb/smile2.gif

------------------
Rich Rohrich
Applied Fluid Dynamics
rich@dirtrider.net
www.eric-gorr.com

Posted by: Bluethumper---------------------

hey rich,if i change my wr can for the yz can what about a spark arrester, the yz can does not have one, is that the reason people are putting after market exhaust systems on them? i never ride on a track, i ride either in the woods or the desert.

------------------
Let me know what you think.

Posted by: Frosty---------------------

Tex, I can only speak from personal experience with my '98 WR, but since we're both from Texas, and probably ride alot of the same terrain, maybe it will be helpful (I'm up in the high plains, but I ride the Texas enduro circuit, including the Houston area).  When I bought my bike in April '98, I immediately ground down the stop and pulled the air box cover.  Don't see how removing the stop completely could help any, and I tend to agree with Rich - it's probably there for a reason.  Shortly after, I bought an FMF pipe, which in my opinion helped smooth out some of the flat spots and added more overall power. I changed to the YZ timing after that, and felt another drastic improvement with no ill effects. I had richened my jetting with the pipe (45 pilot, 172 main) but still felt it was a little lean on bottom.  Just recently, I ordered the WR jetting kit from Stroker -  180 main, 50 pilot, 100 pilot air jet, and a stock YZ needle.  I was skeptical, but the bike flat rips now.  No hesitation, no bogs, revs to the moon.  After a year and a half, I think I'm finally there. Hope this helps.    

Posted by: Rich Rohrich---------------------

If you need a spark arrestor the your out of luck using the YZ can. I'm sure there are a number of YZ riders that changed to an aftermarket can to get an SA, but I'm convinced that the vast majority did it for some perceived horsepower increase that tends not to exist http://dirtrider-forum.com/forums/ubb/smile2.gif If anyone has a newish stock YZ can they want to get rid of let me know. I have a TON of cool stuff to trade for it bike or computer stuff.

Tex - Frosty is right about the jetting, it's a pretty subjective thing. I tried richening the pilot and richening the needle and liked the response better with a 45 pilot and a step richer needle, but the fuel I use and my spastic riding style may be why http://dirtrider-forum.com/forums/ubb/smile2.gif The fuel you use will have a pretty big impact on your final jetting, but the upside is it's a pretty impressive motor even when the jetting is off some, and just flat INSANE when you get it spot on.

------------------
Rich Rohrich
Applied Fluid Dynamics
rich@dirtrider.net
www.eric-gorr.com

Posted by: TexKDX---------------------

I just got some feedback from another WR rider over the phone on the cam timing and the addition of octane booster. He said he liked the YZ cam timing better overall, but he felt it was a little more stall prone.  I asked if he turned up the idle a bit and he said no.  This has been my trick in the past - idle it up so it will pull from a dead stop without applying throttle with judicious clutch control AND will pull second gear at idle without stalling.  A nice low lumpy idle tends to cause lots of woods stalls in my experience.

He also said 104+ octane booster took some of the flat spots out of the powerband.  He said he tried race gas and the bike did not like it too well.  He ran stock jetting, no lid, no baffle, YZ cam timing change, cut stop.

On jetting, Thumper recommended the the 48 pilot and 172 main with their insert in the can.  Their insert db's at 94-95.

Keep the comments coming, we'll have soup soon enough.  Any feedback out there on the ignition differences, YZ/WR?  Rev limit differences?  Thanks!

Posted by: Rich Rohrich---------------------

I did a ton of octane booster (toluene and MMT based) testing over the summer under various conditions on the YZ4 , and I can tell you for a fact that I didn't find one that helped the throttle response over the CORRECT race gas, and in almost all cases the throttle response of straight pump fuel was superior to booster doped fuel. There are LOTS of race fuels that are inappropriate for our purposes, so it's not suprising to hear someone found one that flattened the response. Lots of race fuels designed for low rpm automotive purposes have high levels of aromatic hydrocarbon, and many use 100LL AvGas as their base stock (also high aromatic). Lots of aromatic hydrocarbons, will give you cheap and highly effective knock protection at the expense of THROTTLE RESPONSE. The same holds true for most octane booster products, although they tend not to be cheap when you do the long term math. I'll send some notes on my Octane Booster tests to Okie and see if he wants to post it.  In the short term get yourself a can of VP C14 and cut it with pump fuel at the level that keeps your wallet happy, jet it SHARP, and buy a RAD guage. Running it straight is a little expensive, but it pays BIG dividends in terms of response and jetting precision. If you do cut it you'll find that you can vary the percentage of C14 to account for changes in weather, without touching a jet.

I have a great contact at Phillips now, so I'll be doing some serious  testing of their Unleaded and Leaded race fuels this spring.  COME ON SPRINGTIME !!!!!

  

------------------
Rich Rohrich
Applied Fluid Dynamics
rich@dirtrider.net
www.eric-gorr.com

Posted by: SUnruh---------------------

rich,
you've got me hooked on all this fuel info, so i have to ask you some questions. http://dirtrider-forum.com/forums/ubb/smile.gif  why C14 over C12?  i just looked at the VP web page and other than .670 vs .717 on specific gravity (what the h*ll is that anyway?) and octane being 6 points more (114 wow!).  what is the big differences?  or is that enough of a difference to be a big change in the motor?  also, C12 does not say anything about aromatic, but C14 says 0%.
now, the really tricky question, would C14 run better, worse or not be noticible in my 2smoke?  also, wouldn't lower octane give you better throttle response?

------------------
Steve Unruh - V29 TCHSS
98yz250, 81yz125, 77yz80

Posted by: TexKDX---------------------

OK, here's what I settled on.

- Vortech exhaust insert - supposed to be higher quality/lower (none) maintenance than the Thumper setup, still 94 db
- Richer jetting on the pilot, main, and a YZ needle
- Will change to YZ cam timing specs
- Will cut and re-use the throttle stop; easy to see WOT with the carb off for jetting

That is it for the performance mods.  Other mods are as follows:
- headlight hi/low switch
- rear brake pressure switch
- license plate holder
- billet mirror perch and good folding mirror
- Moose skid plate
- Renthal CR Hi-bends
- Scotts dampner mount and post (have the dampner to swap over)
- ICO computer (ProComp)
- Enduro Engineering handguards
- 1.6 radiator cap (off KX500)
- IMS YZ tank and Ceet seat

My Visa card will never be the same...  Did I miss anything?

Posted by: Rich Rohrich---------------------

Steve wrote  

Quote:

you've got me hooked on all this fuel info, so i have to ask you some questions.   why C14 over C12? i just looked at the VP web page and other than .670 vs .717 on specific gravity (what the h*ll is that anyway?) and octane being 6 points more (114 wow!).  what is the big differences?  or is that enough of a difference to be a big change in the motor?

The big difference is the Hydrogen to Carbon ration of the fuels. Essentially the lower density (high alkylate content)fuels from VP(C14 & C1http://dirtrider-forum.com/forums/ubb/smile10.gif seem to burn quicker which is an advantage at really high rpm  in an engine with a bore as big, and a chamber as thin and flat as the YZ4. The distillation curve and RVP of C-14 seem better suited to really hot weather on my bike. The front end is a little less volatile with C-14. As the weather starts to cool off C-18 seems to work a bit better, but my guess is C-12 would be a better choice overall for the really cool weather. I haven't had the chance to confirm this, but I'm pretty sure I'm right on this. The most responsive combination I've run is C-14 with dimethyl-ether added to make the front end more volatile, but it's kind of a pain in the ass to deal with, plus, Okie makes weird faces when I run this combination because it smells funny http://dirtrider-forum.com/forums/ubb/smile2.gif Ether is a pro-knock compound so I've done most of my testing by adding it to C-18 to make sure I don't frag the motor. The extra oxygen that ether adds makes for some pretty insane transitional response when I get it right.

Steve wrote  

Quote:

  also, C12 does not say anything about aromatic, but C14 says 0%. now, the really tricky question, would C14 run better, worse or not be noticible in my 2smoke?

I think when they changed the C-12 formulation a while back that they increased the aromatic content some, but I believe it is still fairly low.  Your 250 has a much smaller bore, runs much lower RPM, and has a simple clean highly efficient (read fast burning) combustion chamber, so the things that prove to be an advantage for me, won't matter for you. C-12 is a really nice broad range fuel that seems especially well suited to 250 two-strokes. You'll be thrilled with the throttle response when you get the jetting right. As a rule C-12 tends to make the bike run richer than pump fuel in spite of the fact that it's Specific Gravity is MUCH lower than pump fuels. Pump fuels tend to be in the .740 to .775 range.

Steve wrote  

Quote:

also, wouldn't lower octane give you better throttle response?

Octane has NOTHING to do with it , regardless of what the cluless masses may have tried to tell you. There are lots of factors that contribute to throttle response, but from the the Fuel standpoint the basic chemistry of a fuel and the distillation curve along with proper jetting are the keys to throttle response. I get excellent overall response from my big bore YZ4 with straight VP-C18. The engine doesn't really knock on pump fuel  so octane obviously isn't an issue, but it doesn't respond as well. C-18 is expensive and is fairly tough to jet, so C-14 strikes a much better balance with no REAL difference in response, but the engine seems much less sensitive to weather changes with C-14. C-12 is easy to jet and really easy to deal with for most people. There are probably fuels from VP, Phillips, Elf, or any of a number of other companies that are better than C-12, but unless you want make a career out of testing fuels it's pretty hard to beat C-12 on a cost/benefit ratio. Field testing fuels tends to be fairly subjective, and application specific, so broad range fuels like C-12 can save you a lot of time.

------------------
Rich Rohrich
Applied Fluid Dynamics
rich@dirtrider.net
www.eric-gorr.com

Posted by: WoodsRider---------------------

Tex,
You did miss something...one for me!

WoodsRider

Posted by: TexKDX---------------------

Bill,**this thing is a major time sink compared to setting up the KDX let me tell ya.**It would probably be about equal if you take into account sending the DKX suspenders off for a makeover.

The latest time sink was installing the dampner.**The Scotts stuff was fine, but old Yamaha welded the fork stop off center so I had to add an additional stop on one side so the dampner would not bottom out on full lock left.

While I had the bike down I went ahead and checked the head bearings.**Yup, set up too tight and light on grease.

I also removed the overflow tank for the radiator.**Per Baja Designs the bike will "overheat" while warming up with the stock 1.1 cap, so they sent me a 1.6 off a KX500 and said to pull the tank.

Their plate bracket/light is a bit pricey at $35, but it sure goes on clean and looks good.**It wwould be easy to replicate without the light in it.

This afternoon I'll re-jet the carb and install the light switches.**I'm waiting still on the ICO magnet, hand guard adapters, and grips.**I can get it together without these if needed to test out the motor mods and will do so if the parts don't show up from the Parts Fairy this afternoon (UPS).<p align=right>01-07-2000 :Edited

Posted by: TexKDX---------------------

Rich, which "big bore" is in your YZ4?  A 426 or 450?  Also, any comments on the overflow tank removal?  Thanks.

Posted by: Rich Rohrich---------------------

I currently have the 417 (94mm) Wiseco in my motor, but I'm going to do a second barrel and cylinder head for it with a 441 (97mm) Wiseco piston.

------------------
Rich Rohrich
Applied Fluid Dynamics
rich@dirtrider.net
www.eric-gorr.com

Posted by: WoodsRider---------------------

Leo,
I made my own license plate bracket from my old Texas M/C inspection sticker bracket.  The bracket is made from thin aluminum and Stubb's used to sell them for $5.00.  I beefed it up by cutting an old rubber mud flap to the same shape and placed it between the bracket and plate.  Then I mounted a license light from Auto Zone.  There's a couple of mounting holes on the underside of the KDX fender and the light draws very little amperage.  I'll probably take it off during an enduro and mount the plate to the fender.

Bill

Posted by: MWEISSEN---------------------

TexKDX,
I've got my WR part of the way from where you're going to take your's - Vortip, changed t.stop, removed aibox cover and IMS seat/tank combo.  I'm planning on the jets and YZ timing.  Since you're in Texas and will be riding your bike sooner than me in Michigan, I'd love to hear your results!

Posted by: TexKDX---------------------

MWIESSEN, what part of MI?**Is that your full last name??**I have an old friend named John Weissenborn from the Detroit area who is about the right age to be a re-entry rider.

Anyway, I got is all done as of yesterday AM and took it for a short street/trail ride this afternoon.**A few observations:

1) the WR/YZ motor is suprisingly smooth on the street.**It has enough grunt to chug around like a thumper 0-40 mph.**Anything above 40 and its revvy nature comes out.**I'll probably pick up a larger coutershaft sprocket for trips like Copper Canyon and Monterrey.
2) I like the exhaust note.**Not too noisy but sounds good when you rev it up onto the cam.
3) correcting the air screw setting from 3/8 of a turn to 1 and 1/2 got rid of the stumble on bottom.
4) yes, it IS EASIER TO STALL than with the stock cam timing, no question.**It doesn't just stall, it like backfires and stalls.**My guess this is from the 11.5:1 compression and the short stroke.**Now, you can ride thru this, but make sure to keep the revs up and use the clutch (aka two stroke, gee have we heard this before...)
5)The bike impresses me with how easy it is to start.**After completely draining the carb and the bike sitting for a week I turned on the gas, filled the bowl, twisted the throttle 3 times, kicked it thru with the compression release pulled 5 times, and choke on it started on the first kick.**Wow.
6) The Moose skidplate is great for 53 bucks.**The WR lacks clearance compared to my KTM and the plate is a good idea.
7) If you take your time, the bike is not bad to work on.**Not as easy as a 2 stroke or my old LC4, but not all that bad.**Just keep the manual handy.
http://dirtrider-forum.com/forums/ubb/smile10.gif The seat/tank combo is nice. The Ceet foam and shape is a definate improvement over stock.
9) I documented the whole thing with my digital camera, dual sport conversion too, so let me know if you need the pix.
10) The motor comes on HARD.**It has enough torque off the cam to act like a thumper with my 160 pound butt, but you are just a fan of the clutch away from 250 2 stroke power.

Hope this helps, TexKDX.<p align=right>01-09-2000 :Edited

Posted by: MWEISSEN---------------------

Hey Tex,
You knew John Weissenborn?  He's my brother, but not from the Detroit area.  Not too many around with that name, so I assume that's who you're talking about.  Let me know who you are (mweissen@aol.com), and I'll tell him you wrote.

Thanks for the stuff on the WR!

Posted by: MWEISSEN---------------------

Tex,
You didn't mention rejetting when you mod'd your bike.  Did you?

Also, check out a new tank and YZ seat.  You'll love that mod as much as any motor work you can do!

Posted by: TexKDX---------------------

TexKDX wrote:

___________________
OK, here's what I settled on.
- Vortech exhaust insert - supposed to be higher quality/lower (none) maintenance than the Thumper setup, still 94 db
- Richer jetting on the pilot, main, and a YZ needle
- Will change to YZ cam timing specs
- Will cut and re-use the throttle stop; easy to see WOT with the carb off for jetting

TexKDX wrote:
(snip)
_________________
- IMS YZ tank and Ceet seat

Yea, I did re-jet to the YZ needle, richer pilot (can't remember the number), and a 172 main.  Love the seat, but I question the plastic compound IMS uses.  It allows gas vapor to seep thru into the air as best I can tell, smelling up the garage.  Has anyone else had this experience?

Where is John now?  He was my customer when he was at DowElanco in Indpls.  Great guy, quite a golfer.  Is he back up in MI??  Does he ever ride?  I'd like to look him up when I'm in Indy next summer or during the Six Days of Michigan.  Stay in touch, TexKDX.

Posted by: MWEISSEN---------------------

>It allows gas vapor to seep thru into the air as best I can tell, >smelling up the garage.  Has anyone else had this experience?

All plastic tanks do that to an extent, but I haven't noticed it with my IMS tank.  Are you using the IMS filler cap, or the stock WR's?  The WR cap fits better and is better quality IMHO.

Text Version Home

This is the text version of DirtRider.Net Click Here for the Full Version

WR400 myths and truths

This is the text version of DirtRider.Net
Click Here for the Full Version